Hydrogen attack Physical

Physical Hydrogen Attack. A related phenomenon is physical hydrogen attack, which may happen simultaneously with chemical attack. It occurs when adsorbed... 

The element has a metallic, bright silver luster. It is relatively stable in air at room temperature, and is readily attacked and dissolved, with the evolution of hydrogen, but dilute and concentrated mineral acids. The metal is soft enough to be cut with a knife and can be machined without sparking if overheating is avoided. Small amounts of impurities can greatly affect its physical properties. 

Limitations of Plasma CVD. With plasma CVD, it is difficult to obtain a deposit of pure material. In most cases, desorption of by-products and other gases is incomplete because of the low temperature and these gases, particularly hydrogen, remain as inclusions in the deposit. Moreover, in the case of compounds, such as nitrides, oxides, carbides, or silicides, stoichiometry is rarely achieved. This is generally detrimental since it alters the physical properties and reduces the resistance to chemical etching and radiation attack. However in some cases, it is advantageous for instance, amorphous silicon used in solar cells has improved optoelectronic properties if hydrogen is present (see Ch. 15). 

The increased use of renewable hydrogen energy can reduce the vulnerability to physical attack, economic attack by OPEC sanctions or embargo, terrorist attacks (since hydrogen dissipates faster than gas or jet fuel), and many cumulative environmental problems. 

Chemical/Physical. At 230 °C, endrin isomerizes to an aldehyde and a ketone. When heated to decomposition, hydrogen chloride and phosgene may be released (NIOSH, 1997) but residues containing an aldehyde (15-20%), a ketone (55-60%), a caged alcohol (5%), and other volatile products (15-20%) were reported (Phillips et al., 1962). In water, endrin undergoes nucleophilic attack at the epoxide moiety forming endrin diol (Kollig, 1993). 

Chemical/Physical. Heptachlor epoxide will hydrolyze via nucleophilic attack at the epoxide moiety forming heptachlor diol which may undergo hydrolysis forming heptachlor triol and hydrogen chloride (Kollig, 1993). 

Water is without effect on the element even at a red heat,3 but the combined action of water and ozone produces telluric acid at the ordinary temperature.4 The action of hydrogen peroxide upon tellurium is influenced considerably by the physical state of the element colloidal tellurium is readily oxidised, but crystalline tellurium is not readily attacked and has first to be dissolved in an aqueous solution of alkali hydroxide, when oxidation becomes possible with formation of tellurate.5 Hydrogen peroxide of 60 per cent, strength reacts very slowly with tellurium at a temperature of 100° C., but with increasing amount of telluric acid formed, the rate of dissolution increases. Amorphous tellurium as ordinarily prepared behaves in a similar manner to the crystalline variety, but if it is dried by treatment with alcohol and ether instead of by heating at 105° C. it will dissolve readily in a concentrated solution of hydrogen peroxide.6... 

In addition to possessing physical properties compatible with car-bene character at C , alkenyl ketone rings with a hydrogen on C are susceptible to nucleophilic attack by PMe3 [Eq. (61)]. A full paper de-scribing several 1 1 adducts and including the structure of Cp(CO)2-... 

Production of sulfides. This may involve the production of FeS, Fe (OH)2 etc. and an aggressive chemical agent such as hydrogen sulfide (H2S) or acidity. Micro-organisms may also consume chemical species that are important in corrosion reactions (e.g., oxygen or nitrite inhibitors). Alternatively, their physical presence may form a slime or poultice, which leads to differential aeration cell attack or crevice corrosion. They may also break down the desirable physical properties of lubricating oils or protective coatings. (Stott)5... 

The committee notes that resilience to terrorist attack has become a major performance criterion for any infrastructure system. In the case of hydrogen, neither the physical and operating characteristics of future infrastructure systems nor the timing of their construction can be understood in sufficient detail to permit an analysis of their vulnerability. However, the committee does observe that public concerns with terrorism seem likely to influence the choice of any future energy system and that resilience to deliberate attack is best designed in at the beginning. 

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